Switching system control arrangements

ABSTRACT

Methods and arrangements for associating control messages received in the D-channel of an integrated services digital network (ISDN) line with the call control process to which the message relates are disclosed. With ISDN, a single control channel, called the D-channel, can be used concurrently to control a plurality of calls. As each call is initiated, a call control process and data structure including the unique identity of the call, are created. The data structures associated with the same D-channel are linked together. When a control message including a given identity is received, the data structures associated with the D-channel conveying the message are searched in sequence until a data structure having the given identity is found. The contents of this data structure are used to access the control process associated therewith. When the search reveals no matching identity and the message is a call setup message, a new process and data structure are created.

TECHNICAL FIELD

This invention relates to data communication systems, and moreparticularly, to arrangements for coordinating control information whena given channel can be used for more than one concurrent communication.

BACKGROUND OF THE INVENTION

Communication systems are known in which a single data channel can beused concurrently for multiple communications. One such type of systemis an Integrated Services Digital Network (ISDN). With ISDN, terminalequipment can be connected to the network by two 64 Kbps channels(B-channel) and one 16 Kpbs channel (D-channel). The B-channelinformation is primarily circuit switched, voice, or data. Theinformation in the D-channel is accumulated in the network to be packetswitched. The D-channel information can be packet switched data or itcan be control information, which is used by the network to control theswitching of the B- and D-channels. Accordingly, the D-channel can beengaged in multiple concurrent communications to control multipleD-channel packet communications and the B-channel communications.Additionally, multiple user terminals may be connected to a singleincoming line increasing even further the number of concurrent uses of asingle D-channel.

Each active communication in a switching system is associated with acall control program and stored data describing the present state of thecommunication. Whenever a call-related stimulus is received, theappropriate data must be located and associated with the appropriatecall control program. When a large number of D-channels is in use andeach is being used for a number of communications, the total amount ofstored call describing data becomes very large. Searching this data forthe appropriate data and call control program becomes a difficult andtime-consuming task. This is particularly troublesome in systems wherethe channel in which the stimulus is received does not uniquely identifythe communication to which it relates. We propose an efficient methodand arrangement for storing communication related data and for searchingsuch data in systems where multiple communications may be controlled byinformation from a single channel.

SUMMARY OF THE INVENTION

The aforementioned problem is solved and a technical advance is achievedin accordance with the principles of the present invention. In anarrangement comprising a plurality of user access lines each connectingat least one user terminal to a switching arrangement, the user accesslines being capable of multiple concurrent communications and each userterminal being associated with at least one data channel for conveyinginformation relating to the communications conveyed by the user accesslines, the method of creating a control process for each communicationin the arrangement; creating a data structure for each activecommunication in the arrangement, each data structure including theunique identity of the associated communication and the identity of thecontrol process associated therewith; transmitting by one of the userterminals a first message relating to a given communication in the datachannel associated with that user terminal, the first message includingthe unique identity of the given communication; and searching inresponse to the first message only those data structures associated withthe data channel conveying the first message to locate the datastructure including the unique identity.

In one embodiment of the present invention the data channel is theD-channel of an ISDN user access line. As data structures are created,they are linked in sequence to other data structures relating tocommunications being controlled by information in the same D-channel.When a message is received, the identity of the D-channel conveying itis used to determine the address of the first of the data structuresassociated with that D-channel. The data structures are then searched insequence, as determined by link addresses, until a data structure isfound having the same unique identity as the received message or the endof the link structure is reached without a matching identity beingfound. When a matching unique identity is found, the identity of theassociated control process is used to access that control process whichmakes use of the received message. Alternatively, when the end of thelink structure is reached without a match, a new control process andassociated data structure are created. The new data structure is linkedto the last of the preexisting data structures relating to the sameD-channel. This new data structure includes the unique identity of thereceived message and the identity of the associated control process.

BRIEF DESCRIPTION OF THE DRAWING

A more complete understanding of the present invention may be obtainedfrom a consideration of the following description when read inconjunction with the drawing in which:

FIG. 1 is a representation of control processes and data structures usedin the present invention;

FIG. 2 is a block diagram of a switching system employing the presentinvention;

FIG. 3 is a flow diagram showing the basic operation of coordinatingmessages with data structures and control processes; and

FIG. 4 is a flow diagram emphasizing an embodiment of one of the actionblocks of FIG. 3.

DETAILED DESCRIPTION

FIG. 2 presents a block diagram of an exemplary switching systemillustrating the principle of the present invention. The system includestwo switching modules 1000 and 2000, to provide both circuit switchingand packet switching service to a plurality of user terminals e.g.,1001, 1002, 2001, representing, for example, customer teleterminals,vendor databases, telephone operator position terminals or packet accessports. Only switching module 1000 is shown in detail in FIG. 2. Eachuser terminal, e.g., 1001, transmits information to and receivesinformation from its associated switching module, e.g., 1000, in two 64kilobits per second channels referred to as B-channels and in one 16kilobits per second channel referred to as a D-channel. In the presentembodiment, the B-channels can be used to convey digitized voice samplesat the rate of 8000, eight-bit samples per second and/or to convey dataat a rate of 64 kilobits per second. Each B-channel is separatelycircuit-switched by the system to other user terminals, e.g., 1002 and2001. The D-channel is used both to convey signaling packets to effectcontrol message signaling between user terminals and the system and toconvey data packets among user terminals. The D-channel ispacket-switched by the system either to other user terminals or to acontrol unit 1017 which controls the establishment of bothcircuit-switched calls and packet-switched calls within switching module1000.

In the present exemplary embodiment, information is conveyed between auser terminal, e.g., 1001, and switching module 1000 via a four-wire,user access line 1003 using one pair of wires for each direction oftransmission. User line 1003 transmits a serial bit stream at the rateof 192 kilobits per second which comprises 144 kilobits per second forthe above-mentioned two 64 kilobits per second B-channels and one 16kilobits per second D-channel and which further comprises 48 kilobitsper second used for a number of functions including framing, DCbalancing, control and maintenance. User line 1003 represents what isreferred to by the International Telegraph and Telephone ConsultativeCommittee (CCITT) as the T-interface. The use of the T-interface in thepresent system is only exemplary. The invention is equally applicable tosystems using other access methods.

In switching module 1000, the user lines, e.g., 1003 and 1004, areterminated by two digital line units 1101 and 1102. Information isconveyed between each of the digital line units 1101 and 1102 and atime-slot interchange unit 1011 via a plurality of 32-channelbidirectional time-multiplexed buses 1201. Information is also conveyedbetween each of the digital line units 1101 and 1102 and a packetswitching unit 1400 via a plurality of 32-channel bidirectionaltime-multiplexed data buses 1202. The buses 1201 are used primarily toconvey B-channel information which is circuit switched by time-slotinterchange unit 1011 either to user terminals served by switchingmodule 1000 or to other switch modules via time-multiplexed switch 10 ina manner well known in the art. However, the buses 1201 are also used toconvey D-channel information which is further conveyed via predeterminedtime-slot interchange unit 1011 channels and via a 32-channelbidirectional data bus 1205 to packet switching unit 1400. Each channelor time slot on the buses 1201 can include eight B-channel bits from oneuser terminal or two D-channel bits from each of four different userterminals. The data buses 1202 are used to convey D-channel information.Each channel or time slot on the data buses 1202 and 1205 can includetwo D-channel bits from each of four different user terminals.

In the present exemplary embodiment, packet switching unit 1400 includesa data fan-out arrangement 1600, 96 protocol handlers 1700-0 through1700-95, and packet interconnect 1800 which interconnects protocolhandlers 1700-0 through 1700-95 and a processor interface 1300. Eachuser terminal, e.g., 1001, is associated with one of the protocolhandlers 1700-0 through 1700-95 and, more particularly, with one of 32High-level Data Link Control (HDLC) circuits, (not shown), included inthat associated protocol handler. In the present embodiment,communication links are established between the HDLC circuits of theprotocol handlers and peer HDLC circuits (not shown) in the userterminals. These links are used to convey packets within HDLC frames inaccordance with the well-known HDLC protocol. The connections between agiven protocol handler and its associated D-channels on data buses 1202and 1205 are completed by data fan-out arrangement 1600.

The packets conveyed on the D-channel communication links between userterminals and associated protocol handlers are of variable length. Eachuser terminal, e.g., 1001, transmits and receives packets in one or morelogical communication channels. The logical channel of a given packet isidentified by a logical channel number which is a part of the header ofthat packet. Each packet received by a protocol handler from a userterminal is stored in a random access memory (RAM), (not shown) in thatprotocol handler. A signaling packet of the type used for call control,includes information defining the packet as signaling information. Apacket which is used for data communication includes informationdefining it as a data packet. A protocol handler sends signaling packetsto processor interface 1300 via a packet interconnect 1800. Processorinterface 1300 is similar in structure to protocol handlers 1700-0through 1700-95. It receives and buffers data packets from packetinterface 1800 and notifies control unit 1017 when a packet is received.Processor interface 1300 also receives information from control unit1017 and prepares packets for transmission to packet interface 1800. Ifa packet received from a user terminal, e.g., 1001, is a data packet,and a packet-switched call has previously been established, it istransmitted via packet interconnect 1800 to the protocol handlerassociated with the destination user terminal for subsequenttransmission thereto. (If the packet-switched call is establishedbetween two user terminals that are associated with the same protocolhandler, the data packets need not be transmitted via packetinterconnect 1800. Instead, the protocol handler simply transmits thedata packets in the appropriate channel to the destination userterminal.)

When a given protocol handler, e.g., 1700-0, has received a completepacket from a user terminal and has determined the destination of thatpacket, i.e., either one of the other protocol handlers or processorinterface 1300, it transmits a logic zero Request To Send (RTS) signal,also referred to herein as a request signal, on one conductor of asix-conductor bus 1701-0 to packet interconnect 1800. Similarly, whenprocessor interface 1300 has a packet ready for transmission to one ofthe protocol handlers, it transmits a logic zero RTS signal on oneconductor of a six-conductor bus 1301. Packet interconnect 1800 enableseach of the protocol handlers and the processor interface 1300 totransmit in a predetermined sequence. Since processor interface 1300transmits signaling packets to all of the user terminals served byswitching module 1000, the sequence effected by packet interconnect 1800enables processor interface 1300 sixteen times for each enabling of anindividual protocol handler. When the packet interconnect 1800 sequencereaches protocol handler 1700-0, packet interconnect 1800 responds tothe RTS signal on bus 1701-0 by transmitting a logic zero Clear To Send(CTS) signal, also referred to herein as a clear signal, on a secondconductor of bus 1701-0 to protocol handler 1700-0. Protocol handler1700-0 responds to the CTS signal by transmitting its stored packet at ahigh rate, e.g., 10 megabits per second, via packet interconnect 1800 toits destination. All of the protocol handlers and the processorinterface 1300 can receive the packet, but in the present embodiment,typically only one destination as defined by the packet header actuallystores the packet for subsequent use or transmission. Only after thecomplete packet has been transmitted by protocol handler 1700-0, doesthe packet interconnect 1800 sequence resume. The receipt of the packetby the destination protocol handler or by processor interface 1300 isacknowledged by the transmission of an acknowledgement packet back toprotocol handler 1700-0. Switching module 2000 is substantiallyidentical to switching module 1000. The protocol handlers 1700-0 through1700-95 and the processor interface 1300 in switching module 1000 arereferred to herein as packet switching nodes since they accumulatereceived data bits into packets and subsequently transmit the packets ontoward their destinations. In the present example, protocol handlers1700-0 and 1700-2 through 1700-95 are connected to the D-channels fromuser terminals and are referred to as user packet switching nodes. Sinceprocessor interface 1300 is connected to convey control information toand from control unit 1017, processor interface 1300 is referred to as acontrol packet switching node. One protocol handler in each switchingmodule, e.g., protocol handler 1700-1 in switching module 1000 is usedfor switching data packets for inter-module packet calls and is referredto as an intermediate packet switching node.

In the present embodiment, four channels on data bus 1205 are connectedat system initialization by time-slot interchange unit 1011 to fourchannels, e.g., channels 109 through 112, at input/output port pair P55of time-multiplexed switch 10. Time-multiplexed switch 10 includesinformation defining that a bidirectional communication path is to beestablished between input/output port pairs P55 and P61 during channels109 through 112 of each time-multiplexed switch 10 cycle. By the use ofthese predefined connections, protocol handler 1700-1 can transmitcommunication packets with switch module 2000.

Control unit 1017, in cooperation with central control 30, controlsswitching functions relating to the user terminals, e.g., 1001 and 1002,connected to switching module 1000. Control unit 1017 communicates withcentral control 30 using control channels through time-multiplexedswitch 10 and control distribution unit 31 in a known manner. When aconnection is to be established in switching module 1000, a call controlprocess is created in control unit 1017. This call control process isuniquely associated with the requested call and is used to accumulateand distribute information to complete and record the call. Thefollowing is a discussion of the methods and arrangements employed inthe present embodiment for associating call control processes with callsand for finding the correct process to handle switching functions whenthe need arises. When a user terminal, e.g., 1001, wishes to establish acall, it first formulates a packet, called a setup packet, to betransmitted in the D-channel associated with user terminal 1001. Thissetup packet includes several fields in addition to the actual callsetup message. Among these additional fields is a Terminal EndpointIdentifier (TEI), a Service Access Point Identifier (SAPI) and a callreference value. Each user terminal is associated with at least one TEI.Additionally, it is possible that a given user terminal may comprisemore than one terminal endpoint and thus be associated with more thanone TEI. The TEIs are selected such that no two user terminals connectedto the same user access line have the same TEI. The SAPI is used toidentify the type of message containing it. In the present embodiment,an SAPI of 0 indicates that the associated message is a signalingmessage, an SAPI of 16 indicates that the associated message is a packetswitching data or control message. Thus, a call setup packet includes anSAPI of 0 indicating that it is the signaling packet. The call referencevalue is selected by user terminal 1001 to distinguish the call fromother D-channel calls from the same user terminal. It should be notedthat with regard to a given D-channel the combination of the TEI andcall reference value uniquely identify a call.

Once the setup packet is formulated, it is transmitted (block 4050, FIG.3) to digital line unit 1101 in the D-channel of user access line 1003.Digital line unit 1101 in cooperation with data fanout 1600, routes thepacket to a predetermined HDLC circuit (not shown) of a predeterminedprotocol handler, e.g., 1700-0, of packet switching unit 1400. Theprotocol handler 1700-0 reads the SAPI to determine the type of theassociated message. Since the packet is a signaling packet, protocolhandler 1700-0 formulates a packet to be sent to processor interface1300. The packet to be transmitted includes most of the information ofthe received packet, and additionally includes the identity of theprotocol handler 1700-0 (PHI), the identity of the particular HDLCcircuit (HDLCI), and the particular D-channel, e.g., D-1, being used forthe call. After formulation, the new packet is transmitted (block 4051,FIG. 3) to processor interface 1300 via packet interconnect 1800 asdiscussed above. Processor interface 1300 receives and stores thesignaling packet and notifies control unit 1017 of its arrival (block4052, FIG. 3). In the present embodiment, each active call is associatedwith a call control process in control unit 1017. This call controlprocess remains until the call associated therewith is disconnected. Thecall control process responds to stimuli from various controllers anduser terminals to set up, maintain, and disconnect the call that it isassociated with. Accordingly, a given process must respond to allstimuli relating to its associated call. Efficiently finding theparticular call control process for each incoming D-channel packet is adifficult problem especially when more than one call can be controlledby the same D-channel.

When a call control process is created, a data structure is also createdwhich contains the identity of the associated process. In the presentexample, a data structure is created by allocating a previouslyinitialized memory block. FIG. 1 represents the association of controlprocesses, e.g., 4000, and data structures, e.g., 4001. Each controlprocess and the associated data structure is associated with aparticular user terminal, e.g., 1001 (FIG. 2), and is accordinglyassociated with a particular D-channel. In accordance with the presentembodiment, each data structure, e.g., 4001, contains the processidentity (PID) 4015 of the associated control process as well as the TEI4016, the call reference value 4017, the HDLCI 4018, and the PHI 4019 ofthe call being served by the process. Additionally, each data structureis sequentially linked by a link address 4020 to a data structureassociated with a call using the same D-channel. The first datastructure associated with a given D-channel is pointed to by informationstored in a D-channel table 4006. D-channel table 4006 comprises aplurality of entries each entry relating to an existing D-channel, andbeing labeled from D-1 to D-n. Each entry e.g. 4021 in the D-channeltable has associated therewith the address of the first data structureassociated with the identified D-channel. FIG. 1 represents three callcontrol processes 4000, 4002, and 4004, and their respectivelyassociated data structures, 4001, 4003, and 4005, all being associatedwith a D-channel D-1. The address stored in location 4021 of D-channeltable 4006, which is associated with D-channel D-1 points to the datastructure 4001, which in turn is linked to data structure 4003, which isin turn linked to data structure 4005. It will be noted that datastructure 4005 is linked to no subsequent data structure and its linkstorage area 4022 is marked END. FIG. 1 also represents the controlprocesses 4007 and 4009, which are respectively associated with thelinked data structures 4008 and 4010. The last-named processes and datastructures are associated with D-channel D-n as shown in D-channel table4006.

It will be remembered that a signaling packet was sent to processorinterface 1300 identifying D-channel D-1 in response to a call setupmessage from user terminal 1001. This packet is stored in processinterface buffer 4011. Additionally, control unit 1017 was notified ofthe arrival of this packet. Control unit 1017 responds to this notice byreading the D-channel identifying portions of the received packet (block4053, FIG. 3) and using this information to access D-channel table 4006to find the address of the first data structure associated with channelD-1 (block 4054, FIG. 3). This address is used to access data structure4001 (block 4055, FIG. 3) as indicated by arrow 4012. As previouslystated, the TEI and call reference value included in a data structureuniquely identify the particular call associated with that datastructure. The TEI 4016 and call reference value 4017 stored in datastructure 4001 are compared (block 4056, FIG. 3) with the TEI and callreference value contained in the packet stored in interface buffer 4011.There will be no match since the incoming packet is the first messagerelating to a call and no data structure should yet have been createdfor this call. Accordingly, the link value 4020 stored in data structure4001 is used to access data structure 4003 (block 4058, FIG. 3). Again,a comparison is performed and no match is found. These comparisonscontinue with subsequent data structures, e.g. 4005, until a link value4022 defining the end of the link structure is found (block 4057, FIG.3). Control unit 1017 responds to the END link value 4022 found in datastructure 4005 by checking (block 4067, FIG. 3) to determine if themessage relates to a new service request. Since, in the present example,the incoming message is a call setup message, a new call control process4013, and an associated data structure 4014 are created (block 4059,FIG. 3). The new data structure 4014 and control process 4013 are shownas dotted boxes in FIG. 1. The new process 4013 is linked 4023 to thenew data structure 4014 and the data structure is linked (not shown inFIG. 1) to data structure 4005 (block 4060, FIG. 3). Additionally, theTEI 4024, call reference value 4025, HDLCI 4026, and PHI 4027 from thesignaling packet in processor interface buffer 4011 are stored in thedata structure as well as a link address END 4028 defining the end ofthe link structure. Certain special services may be provided withmessages which do not require individual control processes. Accordingly,when the end of a linked structure is found and the received message isnot a new service message, a check is performed (block 4063, FIG. 3) todetermine if the message is a special service request or an error.

When the signaling packet stored in interface buffer 4011 relates to anexisting call, the data structures associated with the D-channel of thecall are searched in sequence until a match of the TEI and callreference value occurs. The process identity PID of the data structurewith the matching values is used to access (block 4061, FIG. 3) theassociated control process. Such accessing may consist of notifying theidentified process of the message in interface buffer 4011. Theassociated control process then reads processor interface buffer 4011and utilizes this information to establish, maintain, or releaseconnections.

Control unit 1017 can also transmit signaling messages to userterminals. To do so, the relevant call control process accesses itsassociated data structure to determine the TEI, call reference value,HDLCI, and PHI associated with the call. This information is used toconstruct a packet, which is sent via the processor interface 1300 topacket switch unit 1400 and then to the defined user terminal asabove-described.

As previously stated, every user terminal has a TEI which is unique on agiven user access line. By convention, a predetermined TEI, called thebroadcast TEI is never associated with a specific user terminal. Thebroadcast TEI is used when a control unit, e.g., 1017 receives anexternal request for communication. The following example in conjunctionwith FIG. 4 relates to the use of the broadcast TEI and also shows amore detailed embodiment of the search method described with regard toFIG. 1. In accordance with the present example, an external request forcommunication is received defining the user access line 1003. When sucha request is received, control unit 1017 creates a call control process,e.g., 4004, and a data structure, e.g., 4005, as above-described, andlinks the data structure to other data structures associated with thesame D-channel. From data stored in the control unit 1017, the HDLCI andPHI for the connection are determined. Control unit 1017 then stores inthe data structure the broadcast TEI, a call reference value selected bycontrol unit 1017, and the HDLCI and PHI as determined above. A callsetup packet is formulated using this information which packet istransmitted to the destination D-channel on user access line 1003 asabove-described. All user terminals connected to a given user accessline can, by convention, respond to the broadcast TEI. Accordingly, userterminal 1001 receives and responds to the signaling packet includingthe broadcast TEI. In order to specifically identify the new call, userterminal 1001 returns a signaling packet (alerting message) to theprocessor interface 1300 having the call reference value selected bycontrol unit 1017 and including the TEI of user terminal 1001 (not thebroadcast TEI). Control unit 1017 responds to the alerting message bysearching the data structures associated with the D-channel identifiedby the alerting message. FIG. 4 is a flow diagram of a more detailedsearch method. The dotted block labeled 4056 in FIG. 4 can besubstituted for action block 4056 of FIG. 3. In FIG. 4, the actionblocks having the same function as equivalent action blocks in FIG. 3are given the same numerical designation.

Initially, the call reference value 4017 of data structure 4001 iscompared (block 4070, FIG. 4) with the call reference value of thereceived packet. There will be no match and the next data structure 4003will be searched as previously described. When data structure 4005 issearched, the call reference values will match. Then a comparison (block4071, FIG. 4) is made to determine if the TEIs match. In the presentexample, the TEIs will not match since the stored broadcast TEI does notmatch the TEI of user terminal 1001. Accordingly, a check is performed(block 4072, FIG. 4) to determine if the stored TEI is the broadcastTEI. Since the stored TEI is the broadcast TEI, the stored TEI isreplaced (block 4073, FIG. 4) with the TEI in the packet from userterminal 1001 and the control process associated with the data structurebeing searched is accessed (block 4061, FIG. 4). All further packetsrelating to this call will include the TEI of user terminal 1001 nowstored in the data structure 4005.

If it were found in block 4072, FIG. 4, that the stored TEI did notmatch the broadcast TEI, then the search sequence would continue byreturning to action block 4057 to determine if the end of the list hadbeen found. Additionally, if there had been a match of TEIs in block4071, the procedure would have accessed the associated process (block4061, FIG. 4) as described above.

What is claimed is:
 1. In an arrangement comprising a plurality of useraccess lines each connecting at least one user terminal to a switchingarrangement, said user access lines being capable of multiple concurrentcommunications each having a unique identity and each user terminalbeing associated with at least one data channel for conveyinginformation relating to the communications conveyed by the user accesslines, the method comprising the following steps:creating a controlprocess for each active communication in said arrangement; creating adata structure for each active communication in said arrangement, eachdata structure including the unique identity of the associatedcommunication and the identity of the control process associatedtherewith; transmitting by one of said user terminals a first messagerelating to a given communication in the data channel associated withthat user terminal, said first message comprising the unique identity ofthe given communication; and searching, in response to said firstmessage, only those data structures associated with the data channelconveying said first message to locate the data structure including theunique identity of said given communication.
 2. The method in accordancewith claim 1 further comprising the step ofaccessing the control processidentified in the data structure located in said searching step.
 3. Themethod in accordance with claim 1 further comprising the following stepswhen said searching step fails to locate a data structure including theunique identity of said given communication:creating a call controlprocess for said given communication; and creating a data structure forsaid given communication said data structure including the uniqueidentity of said given communication and the identity of the controlprocess associated with said given communication.
 4. The method inaccordance with claim 1 further comprising:linking each data structureto other data structures associated with the same data channel and saidsearching step comprises: identifying a first of said data structuresassociated with the data channel conveying said first message; andsearching said first of said data structures and each data structurelinked thereto until a data structure including the unique identity ofsaid given communication is found.
 5. The method in accordance withclaim 1 further comprising the steps of:reading, by a first controlprocess, the unique identity of the communication included in the one ofsaid data structures associated with said first control process; andtransmitting a second message in the data channel associated with saidfirst control process, said second message comprising the uniqueidentity of the communication associated with said first controlprocess.
 6. In an arrangement comprising a plurality of terminal endpoints, each having a unique terminal end point identifier, connected toa switching network by access lines, said access lines being capable ofa plurality of concurrent communications, each communication beingassociated with a data channel for conveying control information packetsto said switching network for controlling connections therethrough, themethod comprising:creating a control process for each communication insaid network; creating a data structure for each communication in saidnetwork, each data structure including the terminal end point identifierof the terminal end point of the associated communication, a callreference value, and the identity of the control process of theassociated communication; transmitting, by a given one of said terminalend points, a control information packet relating to a givencommunication in the one of said data channels associated with saidgiven communication, said control information packet including theterminal end point identifier of the given terminal end point and a callreference value; searching, in response to said control informationpacket, only those data structures relating to communications associatedwith the data channel conveying said control information packet tolocate a data structure including the same terminal end point identifierand call reference value included by said control information packet. 7.The method in accordance with claim 6 further comprising the stepofaccessing the control process identified in a data structure locatedin said searching step.
 8. The method in accordance with claim 6 whereinsaid transmitting step comprises:transmitting by a given one of saidterminal end points a control information packet relating to a givencommunication in the one of said data channels associated with saidgiven communication, said control information packet including theterminal end point identifier of the given terminal end point and a callreference value selected by the terminal end point and said methodfurther comprises the following steps when said searching step fails tolocate a data structure including the same terminal end point identifierand call reference value included by said control information packet:creating a control process for said given communication; and creating adata structure for said given communication, said data structureincluding the terminal end point identifier and call reference valueincluded in said control information packet and the identity of thecontrol process associated with said given communication.
 9. The methodin accordance with claim 6 further comprising:linking each datastructure to other data structures associated with the same data channeland said searching step comprises: identifying a first of said datastructures associated with the data channel conveying said controlinformation packet message; and searching said first of said datastructures and each data structure linked thereto until a data structureincluding the same terminal end point identifier and call referencevalue included by said control information packet is found.
 10. In acommunication system having a plurality of channels, a lesser pluralityof said channels being capable of conveying data for a plurality ofconcurrent communications, each communication having a unique identity,an arrangement comprising:a control process associated with eachcommunication in said arrangement; a data structure associated with eachcommunication in said arrangement each data structure including theunique identity of the communication and call control process associatedtherewith; means for transmitting a message for a given communication ina given one of said lesser plurality of channels, said messagecomprising the unique identity of said given communication; andsearching means responsive to said message for searching only those datastructures associated with said given one of said lesser plurality ofchannels to identify a control process associated with said givencommunication.
 11. The arrangement in accordance with claim 10 whereineach data structure is linked to the other data structures associatedwith the same channel; and said searching means comprisesmeans foridentifying a first of said data structures associated with said givenone of said lesser plurality of channels; and means for searching eachlinked data structure until a data structure including the uniqueidentity of said given communication is found.
 12. The arrangement inaccordance with claim 10 further comprising control means operative whenno data structure is associated with said given communication saidcontrol means comprising means for creating a call control process forsaid given communication; andmeans for generating a data structure forsaid given communication said data structure including the uniqueidentity of said given communication.